Escape sequences and XML decimal entities are good for inserting obscure Unicode characters that aren't available on a standard keyboard. For example, if you type in Δ, you get the Greek letter Δ. Or if you type in ♥, you'll get a ♥. Ubuntu users (and users of many other distros of Linux) have access to a program called gucharmap, which is installed by default - it's useful as a "cheat sheet" for these codes. Of course, a quick Google search should do the job, too.
Lastly, this is a handy bit of HTML code that you can stick into your journals and deviantID. It inserts an image link into the lower left hand corner of your profile page. Thanks to Twarri- I mean, paradigm-shifting for the idea. EDIT: Hmm, so apparently, this isn't working anymore, at least not in the sense it used to.
<div id="barkbox"><a class="external external" href="insert link here"><img src="insert image URL here"/></a></div>
My profile page has an example of this, as does paradigm-shifting's. EDIT: See previous edit.